When we drink less water or we are dehydrated the body will compensate for 1-2% of the total amount of water by creating a sensation of thirst. The kidneys, brain, hormones and glands work in co-ordination monitoring the amount of water consumed to the amount of water lost.
The hypothalamus gland regulates the temperature of our body and balances the processes to control the amount of fluids in body. On detecting less amount of water in blood the hypothalamus gives signals for releasing the anti-diuretic hormone which causes kidneys to remove lesser amount of water from the blood. As a result of this we urinate less and the urine is concentrated dark in appearance. The brain also signals to consume water or liquid to bring the hydration level of the body to normal.
Each cell expresses, or turns on, only a fraction of its genes. The rest of the genes are repressed, or turned off.
The turned on genes are then first transcribed into messenger RNA by the process of Transcription.
Then the mRNA is Translated into protein by the process called Translation.
This is how the specific genes are expressed.
